Organic EL display device having organic soluble derivative layer

ABSTRACT

An organic EL display device includes first and second electrodes with a light-emitting layer interposed therebetween and an organic soluble derivative layer arranged between the first electrode and the light-emitting layer, wherein the organic soluble derivative layer prevents impurities from being diffused to the light-emitting layer.

CROSS REFERENCE

This application is a continuation of prior U.S. patent application Ser.No. 10/167,651, now U.S. Pat. No. 6,853,147 filed on Jun. 13, 2002,which claims the benefit of Korean Application No. 2001-74703, filed onNov. 28, 2001, both of which are hereby incorporated by reference forall purposes as if fully set forth herein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.2001-74703 filed on Nov. 28, 2001, in the Korean Industrial PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic electroluminescent (EL)display device, and more particularly, to an organic EL display devicehaving an organic soluble derivative layer.

2. Description of the Related Art

An organic EL display device includes an anode, a hole injection layer,a hole transporting layer, a light-emitting layer, an electrontransporting layer, an electron injection layer, and a cathode which aresequentially stacked on a substrate. In the case of an organic ELdisplay device comprising a low-molecular material, the above-describedlayers are formed using a vacuum deposition technique. In the case of anorganic EL display device comprising a polymer, the above-describedlayers are formed using a spin-coating technique, which placeslimitations on forming the light-emitting layer thereof.

FIG. 1 shows a cross-sectional view of a conventional organic EL displaydevice comprising a high-molecular material, such as a polymer. Theorganic EL display device includes an anode 10, a hole injection layer12, a light-emitting layer 14, and a cathode 16 which are stacked insequence as shown.

The hole injection layer 12 is formed using a spin coating technique,and has a structure such that the hole injection layer 12 is notdissolved in an organic solvent during a spin coating operation to formthe light-emitting layer 14. As a result, an interface characteristicbetween the hole injection layer 12 and the light-emitting layer 14deteriorates. In addition, water or inorganic and organic impuritiesaffect the light-emitting layer 14, thereby lowering stability andshortening a life span of a resulting device.

U.S. Pat. No. 5,247,190 discloses an organic EL display device includingan anode electrode and a cathode electrode with a light-emitting polymerinterposed therebetween. The organic EL display device of U.S. Pat. No.5,247,190 has a disadvantage in that a light-emitting efficiency is lowand a life span is short because a work function of the two electrodesis not approximate or identical to a highest occupied molecular orbital(HOMO) value and a lowest unoccupied molecular orbital (LUMO) value ofthe light-emitting polymer.

In order to overcome the problem, the cathode electrode is made of ametal having a work function similar to the LUMO value of thelight-emitting polymer. However, since the anode electrode has to bemade of a transparent conductive material, there are many restrictionsto using an anode electrode material.

Accordingly, a water-soluble material such as PEDOT (mixture of apoly(3,4)-ethylenedioxythiophene and a polystyrenesulfonate) or PANI(mixture of a polyaniline and a polystyrenesulfonate), available fromBayer AG and Allied Signal, respectively, is deposited on the anodeelectrode using a spin coating technique in order to form a holeinjection layer. The hole injection layer buffers an interface betweenthe anode electrode and the light-emitting polymer, thereby increasing alight-emitting efficiency, a driving voltage and a life span.

However, the PEDOT and the PANI are ionic materials which dissolve inwater and are high in absorptiveness. Thus, even though a firing processis performed after the spin coating operation, it is almost impossibleto remove the water remaining on a surface thereof. In particular, sincethe PEDOT and the PANI show a strong acidity when water exists therein,a reduction is likely to occur on an interface between the holeinjection layer and the light-emitting polymer.

In addition, the PEDOT and the PANI provide poor adhesion to thelight-emitting polymer. Therefore, where the light-emitting polymer ispatterned to form a light-emitting layer, the light-emitting layerhaving a bad pattern characteristic is formed.

Currently, much research is being conducted to improve an interfacecharacteristic between a hole injection layer and a light-emitting layerby introducing a surfactant or an adhesive.

On the other hand, U.S. Pat. No. 5,998,085 discloses a method of formingR, G and B light-emitting layers of an organic EL display device using alaser induced thermal imaging (LITI) technique. The LITI techniquerequires at least a light source, a transfer film and a substrate. Lightemitted from the light source is absorbed by a light absorbing layer ofthe transfer film and is converted into a heat energy. An image formingmaterial on the transfer film is transferred to the substrate by theheat energy to thereby form a desired image. The LITI technique is alsoused to form a color filter of a liquid crystal display (LCD) device anda light-emitting layer.

However, a conventional LITI technique shows a bad transfercharacteristic. Therefore, there is a need for a material and astructure which improve a transfer characteristic of a light-emittingpolymer of an organic EL display device.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anorganic EL display device having a high light-emitting efficiency and animproved life span.

It is another object of the present invention to provide an organic ELdisplay device having an excellent light-emitting layer pattern.

Additional objects and advantages of the invention will be set forth inpart in the description which follows and, in part, will be obvious fromthe description, or may be learned by practice of the invention.

To achieve the above and other objects of the present invention, thereis provided an organic EL display device comprising first and secondelectrodes with a light-emitting layer interposed therebetween, and anorganic soluble derivative layer arranged between the first electrodeand the light-emitting layer, wherein the organic soluble derivativelayer prevents impurities from being diffused to the light-emittinglayer.

There is also provided an organic EL display device comprising first andsecond electrodes with a light-emitting layer interposed therebetween,and at least one organic soluble derivative layer arranged between thefirst electrode and the light-emitting layer, wherein the organicsoluble derivative layer increases an adhesion of the light-emittinglayer.

The organic soluble derivative layer includes a synthetic polymer or amixture which may also have a hole transporting ability, and has asolubility of more than 10 g/L to an organic solvent.

The synthetic polymer is one polymer selected from a group consisting ofan arylamine-based polymer, a perylrene-based polymer, and apyrrole-based polymer, and the mixture includes at least one opticallyinert polymer and at least one arylamine-based low-molecular material.

The optically inert polymer is one selected from a group consisting of apolystyrene, a poly(styrene-butadiene)copolymer, apolymethylmethacrylate, a polyalphamethylstyrene, astyrene-methylmethacrylate copolymer, a polybutadiene, a polycarbonate,a polyethyleneterephthalate, a polyestersulfonate, a polysulfonate, apolyarylate, a fluorinepolyimide, a transparent fluoric resin, and atransparent acrylic resin; and the arylamine-based low-molecularmaterial is one selected from a group consisting of TPD(N,N′-diphenyl-N,N′-di-m-tolyl-biphenyl-4,4′-diamine), NPB, MTDATA(4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine), TDATA(4,4′,4″-tris(N,N-diphenylamino)triphenylamine), and TDAPB(1,3,5-Tris[N,N-bis-(4-methoxyphenyl)aminophenyl]benzene) availablefrom, for example, Sigma-Aldrich Corporation.

The mixture includes the arylamine-based low-molecular material of 10 wt% to 80 wt % dispersed in the optically inert polymer.

The organic soluble derivative layer has a thickness of 1 nm to 50 nm.

The light-emitting layer is patterned using a laser inducedtransfer/thermal imaging (LITI) technique.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome apparent and more readily appreciated from the followingdescription of the embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 is a cross-sectional view of a conventional organic EL displaydevice comprising a polymer;

FIG. 2 is a cross-sectional view illustrating an organic EL displaydevice according to an embodiment of the present invention; and

FIG. 3 is a partial perspective view illustrating a method of patterninga light-emitting layer using a LITI technique according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures.

FIG. 2 shows a cross-sectional view illustrating an organic EL displaydevice according to an embodiment of the present invention. The organicEL display device includes an anode 20, a hole injection layer 22, anorganic soluble derivative layer 24, a light-emitting layer 26, and acathode electrode 28 which are stacked in sequence.

The organic soluble derivative layer 24 prevents impurities from beingdiffused from the hole injection layer 22 to the light-emitting layer 26without lowering a hole transporting ability, thereby improving aperformance characteristic of a resulting device. The organic solublederivative layer 24 has an excellent adhesion to the light-emittinglayer 26. Accordingly, when the light-emitting layer 26 is patterned bya LITI technique, the light-emitting layer 26 has an excellent patterncharacteristic.

The organic soluble derivative layer 24 includes a synthetic polymerwhich may have a hole transporting ability or a mixture which may have ahole transporting ability, and has a relatively high solubility to anorganic solvent, such as a benzene or a toluene. The organic solublederivative layer has a solubility of, for example, more than 10 g/L. Thesynthetic polymer includes a PVK available from Sigma-Aldrichcorporation, a BFE available from Dow chemical company, anarylamine-based polymer, a perylrene-based polymer, and a pyrrole-basedpolymer.

The mixture comprises an arylamine-based low-molecular material and anoptically inert polymer.

The arylamine-based low-molecular material includes TPD, NPB, MTDATA,TDATA, and TDAPB available from, for example, Sigma-Aldrich Corporation.

The optically inert polymer includes a polystyrene, apoly(styrene-butadione)copolymer, a polymethylmethacrylate, apolyalphamethylstyrene, a styrene-methylmethacrylate copolymer, apolybutadiene, a polycarbonate, a polyethyleneterephthalate, apolyestersulfonate, a polysulfonate, a polyarylate, a fluorinepolyimide,a transparent fluoric resin, and a transparent acrylic resin.

The mixture may include the arylamine-based low-molecular material of 10wt % to 80 wt % dispersed in the optically inert polymer.

As a clarification, it is understood that the organic soluble derivativelayer 24 is not to be confused with a conventional hole transportinglayer which may be formed between the hole injection layer and thelight-emitting layers 12 and 14 of FIG. 1. That is, the organic solublederivative layer 24 may be used in addition to a hole transporting layerin an organic EL display, or it may be formulated and used as a layerwhich increases adhesion of and prevents impurities from being diffusedinto the light-emitting layer 26, thereby improving a light-emittingefficiency and life span of the organic EL display, and in addition,serves to transport holes in the organic EL display.

FIG. 3 shows a partial perspective view illustrating a method ofpatterning a light-emitting layer 36 using a LITI technique. A method ofmanufacturing an organic EL display device, with reference to FIG. 3,according to the present invention is described below.

A substrate 30 having an anode is cleaned in, for example, an acetoneand an isopropylalcohol in sequence and is UV/ozone-treated. A holeinjection layer 32 made of PEDOT or PANI is formed on the substrate 30using, for example, a spin coating technique and then heat-treated at atemperature of 200° C. for five minutes. An organic soluble derivativeis dissolved in an appropriate solvent in an appropriate concentrationand stirred for, for example, at least one hour, and then filtered. Theorganic soluble derivative is deposited on the hole injection layer 32using, for example, a spin-coating technique to a thickness of 1 nm to50 nm to thereby form an organic soluble derivative layer 34.

In an organic EL display device, a light-emitting polymer may bedissolved in a solvent which does not dissolve the organic solublederivative layer 34 and deposited using, for example, a spin coatingtechnique to a thickness of tens of nanometer (nm) to form alight-emitting layer.

In the case of a full color organic EL display device, a transfer film40 may be used and aligned with the substrate 30 having the holeinjection layer 32 and the organic soluble derivative layer 34. Thetransfer film 40 includes a light-heat converting layer 44, and aninterlayer insulating layer 46, and a light-emitting polymer layer 36 awhich are sequentially stacked on a transfer substrate 42. Thelight-emitting polymer layer 36 a is transferred from the transfer film40 onto the organic soluble derivative layer 34 using the LITI techniqueto thereby form the light-emitting layer 36. Thereafter, a cathodeelectrode (not shown) is formed on the light-emitting layer 36. Finally,an encapsulating operation is performed to complete the organic ELdisplay device.

A method of manufacturing an organic EL display device having an organicsoluble derivative layer of the present invention is described in detailbelow.

For example, a substrate having an anode is cleaned and thenUV/ozone-treated for 15 minutes. A hole injection layer made of a“PEDOT/PSS,” available from Bayer AG, is spin-coated on the substrate toa thickness of 20 nm to 50 nm at 3,000 rpm. An organic solublederivative of 0.5 wt % available under the trade name “BFE” from DowChemical Company is dissolved in a toluene solvent and stirred for atleast one hour, and spin-coated on the hole injection layer to athickness of 10 nm to 50 nm at 3,000 rpm. Since the toluene does notdissolve the water-soluble hole injection layer, where the organicsoluble derivative layer is coated, it does not damage the holeinjection layer.

A light-emitting polymer of 1.0 wt % to 1.5 wt % available under thetrade name “RED” or “BLUE” from Covion Organic Semiconductors GmbH isdissolved in a toluene solvent and sufficiently stirred, and thereaftera polystyrene having a molecular weight of 2,500 available fromSigma-Aldrich Corporation is mixed as a polymer additive to therebyprepare a mixed solution. A mixing mass ratio of the light-emittingpolymer and the additive is RED:polystyrene=1:1, andBLUE:polystyrene=1:1.5. The mixed solution is sufficiently stirred at atemperature of 60° C. for at least three hours and is spin-coated on atransfer film to a thickness of 80 nm to thereby form a light-emittingpolymer layer.

The light-emitting polymer layer of the transfer film is transferredonto the substrate using a LITI technique to thereby form alight-emitting layer.

Thereafter, a cathode electrode is formed on the light-emitting layer ata high vacuum atmosphere of less than 10⁻⁷ Torr. The cathode electrodeincludes a Ca layer of 50 nm and an Ag layer of 200 nm to 300 nm or aLiF layer of 0.4 nm to 4.0 nm and an Al layer of 100 nm to 600 nm.Finally, an encapsulating operation using a metal can is performed tocomplete the organic EL display device.

In the case of a red light-emitting layer, an edge roughness of thelight-emitting layer patterned by the LITI process is less than 5 μm,leading to an excellent pattern characteristic. When the redlight-emitting layer is used and the cathode electrode includes LiF/Al,a light-emitting efficiency is 1.25 Cd/A, a color coordinate is x=0.67and y=0.32 (CIE 1931, 300 Cd/m² at 6.5 volts), and an expected life spanis 2,000 hours at 100 Cd/m². On the other hands, when the redlight-emitting layer is formed directly on the hole injection layerwithout employing the organic soluble derivative layer, a life span is300 hours at 100 Cd/m².

In the case of a blue light-emitting layer, an edge roughness of thelight-emitting layer patterned by the LITI is less than 10 μm, leadingto an excellent pattern characteristic. When the blue light-emittinglayer is used and the cathode electrode includes Ca/Ag, a light-emittingefficiency is 1.5 Cd/A, a color coordinate is x=0.15 and y=0.1 (CIE1931, 200 Cd/m² at 6.5 volts), and an expected life span is 1,000 hoursat 100 Cd/m². On the other hand, when the blue light-emitting layer isformed directly on the hole injection layer without employing theorganic soluble derivative layer, a life span is 60 hours at 100 Cd/m².

As described above, the organic EL display device having the organicsoluble derivative layer according to the present invention has a highlight-emitting efficiency and an improved life span as compared to aconventional organic EL display device without the organic solublederivative layer. In addition, the organic EL display device of thepresent invention has an excellent light-emitting layer pattern.

Although a few embodiments of the present invention have been shown anddescribed, it will be appreciated by those skilled in the art thatchanges may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe appended claims and their equivalents.

1. A method for fabricating an organic EL display device, the methodcomprising: providing a substrate; forming a first electrode on thesubstrate; forming a light-emitting layer on the first electrode byLaser Induced Thermal Imaging (LITI) method; forming a second electrodeover the light-emitting layer; and forming an organic soluble derivativelayer arranged between the first electrode and the light-emitting layer,wherein the organic soluble derivative layer prevents impurities frombeing diffused to the light-emitting layer.
 2. The method of claim 1,wherein the organic soluble derivative layer includes a syntheticpolymer or a mixture having a hole transporting ability, and has asolubility of more than 10 g/L to an organic solvent.
 3. The method ofclaim 2, wherein the synthetic polymer is one polymer selected from agroup consisting of an arylamine-based polymer, a perylrene-basedpolymer, and a pyrrole-based polymer, and the mixture comprises at leastone optically inert polymer and at least one arylamine-basedlow-molecular material.
 4. The method of claim 3, wherein the opticallyinert polymer is one selected from a group consisting of a polystyrene,a poly(styrene-butadiene)copolymer, a polymethylmethacrylate, apolyalphamethylstyrene, a styrene-methylmethacrylate copolymer, apolybutadiene, a polycarbonate, a polyethyleneterephthalate, apolyestersulfonate, a polysulfonate, a polyarylate, a fluorinepolyimide,a transparent fluoric resin, and a transparent acrylic resin.
 5. Themethod of claim 5, wherein the arylamine-based low-molecular material isone selected from a group consisting of TPD, NPB, MTDATA, TDATA, andTDAPB.
 6. The method of claim 3, wherein the mixture is thearylamine-based low-molecular material of 10 wt % to 80 wt % dispersedin the optically inert polymer.
 7. The method of claim 1, wherein theorganic soluble derivative layer has a thickness of 1 nm to 50 nm. 8.The method of claim 1, wherein the organic soluble derivative layer isformed using a laser transfer induced imaging (LITI) technique or a spincoating method.
 9. The method of claim 1, wherein the organic solublederivative layer increases an adhesion of the light-emitting layer tothe organic EL display device and improves a pattern characteristic ofthe light-emitting layer.
 10. The method of claim 1, wherein the organicsoluble derivative layer prevents impurities from being diffused to thelight-emitting layer without lowering a hole transporting ability.
 11. Amethod for fabricating an organic EL display device, the methodcomprising: providing a substrate; forming a first electrode; forming alight-emitting on the first electrode by Laser Induced Thermal Imaging(LITI) method; forming a second electrode over the light-emitting layer;and at least one organic soluble derivative layer arranged between thefirst electrode and the light-emitting layer, wherein the organicsoluble derivative layer increases an adhesion of the light-emittinglayer to the organic EL display device and prevents impurities frombeing diffused to the light-emitting layer.
 12. The method of claim 11,wherein the organic soluble derivative layer includes a syntheticpolymer or a mixture having a hole transporting ability, and has asolubility of more than 10 g/L to an organic solvent.
 13. The method ofclaim 12, wherein: the synthetic polymer is one polymer selected from agroup consisting of an arylamine-based polymer, a perylrene-basedpolymer, and pyrrole-based polymer, and the mixture comprises at leastone optically inert polymer and at least one arylamine-basedlow-molecular material.
 14. The method of claim 13, wherein: theoptically inert polymer is one selected from a group consisting of apolystyrene, a poly(styrene-butadiene)copolymer, apolymethylmethacrylate, a polyalphamethylstyrene, astyrene-methylmethacrylate copolymer, a polybutadiene, a polycarbonate,a polyethyleneterephthalate, a polyestersulfonate, a polysulfonate, apolyarylate, a fluorinepolyimide, a transparent fluoric resin, and atransparent acrylic resin, and the arylamine-based low-molecularmaterial is one selected from a group consisting of TPD, NPB, MTDATA,TDATA, and TDAPB.
 15. The method of claim 14, wherein the mixture is thearylamine-based low-molecular material of 10 wt % to 80 wt % dispersedin the optically inert polymer.
 16. The method of claim 14, wherein theorganic soluble derivative layer has a thickness of 1 nm to 50 nm. 17.The method of claim 14, wherein the organic soluble derivative layer isformed using a laser transfer induced imaging (LITI) technique or spincoating method.